The specific aims for this project are: Aim #1: Establish a model for clinical data exchanged within and between networks. The first aim of this study is to establish a model for exchange of clinical data within and between clinical research networks involved in HSCT. This model includes: - Creation of a governance structure; - Establishment of business rules; - Development of a data dictionary; and - Definition of a robust, platform-independent messaging system. Aim #2: Implementation of clinical data exchange Implementation will include: - A messaging exchange between the IBMTR and the NMDP; - A messaging link extension of the above to a major U.S. transplant center, the University of Minnesota; and - A messaging link extension to at least one international clinical data registry. Based upon these specific aims, we have developed a series of six specific tasks that comprise the work plan for this proposal.